The present invention relates to catheters for insertion into a body lumen. More particularly, the present invention relates to xe2x80x9cfocalxe2x80x9d balloon dilatation catheters for use in the vascular system. As used herein, xe2x80x9cfocalxe2x80x9d balloons are balloons which focus or concentrate expansive energy at one or more predetermined regions along the surface of the balloon.
Prior art vascular dilatation balloons on typical dilatation catheters tend to fall into one of two broad classes. Most are considered noncompliant balloons, formed from a generally nondistensible material such as polyethylene. The perceived advantage of the noncompliant balloons is that they exhibit a substantially uniform exterior inflated profile which remains substantially unchanged upon incremental increases in inflation pressure. In theory, noncompliant balloons are advantageous because they allow the introduction of increased inflation pressure to break particularly calcified lesions, yet retain a predictable inflated profile so that damage to the surrounding native lumen is minimized.
Certain compliant balloons are also known in the art. A compliant balloon is one which is able to grow in diameter in response to increased inflation pressure. One difficulty with compliant balloons, however, is that inflation within a difficult lesion can cause the balloon to inflate around the plaque to produce a generally hourglass-shaped inflated profile. This can result in damage to the native vessel adjacent the obstruction, while at the same time failing to sufficiently alleviate the stenosis.
In use, both the compliant and noncompliant balloons are generally inflated within a vascular stenosis to a rated inflation pressure. At that pressure, the configuration of most balloons in an unrestricted expansion is cylindrical. The balloon may be subsequently inflated to a higher inflation pressure if that is desirable in the clinician""s judgment. However, the clinician has no effective way to assess the actual inflated diameter of the balloon in vivo based upon the unconstrained in vitro balloon specifications. The in vivo expansion characteristics of the balloon may track or deviate from the in vitro specifications depending upon the morphology of the lesion and the appropriateness of the selected balloon size. The clinician may know only generally or not at all the degree of calcification of the lesion, the symmetry or asymmetry, whether the lesion is soft or resilient, or other variations which affect inflation. In applications where a relatively accurate inflated diameter is desired, such as in certain dilatations or in the implantation of tubular stents, the clinician using prior dilatation balloons thus may not have enough information about the dilatation characteristics of a particular lesion to optimize the dilatation or stent implantation procedure.
Therefore, there exists a need in the art for a vascular dilatation catheter with a balloon which is able to grow predictably in response to increased inflation pressure, and the expansion of which the clinician can observe in real time in comparison to a known diameter reference.
There is provided in accordance with one aspect of the present invention a balloon catheter comprising an elongate flexible tubular body and an inflatable balloon on the tubular body. A proximal segment, a central segment and a distal segment on the balloon are inflatable to a first inflated diameter at a first inflation pressure, and the proximal and distal segment expand to a second, greater inflated diameter at a second greater inflation pressure. The central segment of the balloon remains at a diameter which is less than the second diameter, at the second inflation pressure. In one embodiment, the balloon additionally comprises at least one expansion limiting band on the central segment to limit inflation of the central segment of the balloon. Preferably, the expansion limiting band limits expansion of the central segment to no more than about the first inflated diameter.
In accordance with another aspect of the present invention, there is provided a method of treating a site in a body lumen. The method comprises the steps of providing a catheter of the type having an elongate flexible tubular body and a dilatation balloon on the body. A proximal segment, a distal segment and a central segment of the balloon are inflatable to a first diameter at a first inflation pressure, and the proximal and distal segments of the balloon are inflatable to a second, greater diameter, at a second, greater inflation pressure. The central segment remains substantially at the first diameter at said second inflation pressure.
The catheter is positioned within a body lumen so that the balloon is adjacent a treatment site, and the balloon is inflated to the first inflation pressure. At the first inflation pressure, the proximal segment, the distal segment and the central segment are inflated to no more than about the first inflation diameter.. The balloon is thereafter inflated to a second inflation pressure so that the proximal and distal segments are expanded to the second inflation diameter, while the central segment is simultaneously restrained against further material radial expansion.
Optionally, the foregoing method comprises the additional step of expressing a therapeutic or diagnostic media from the central segment of the balloon to the site in the body lumen.
In accordance with a further aspect of the present invention, there is provided a method of implanting a tubular graft within a body lumen. The method comprises providing an elongate flexible tubular body having an inflatable balloon thereon, the balloon inflatable to a first diameter at a first inflation pressure to produce a generally cylindrical balloon profile, and proximal and distal portions of the balloon are additionally inflatable to a second, larger diameter at a second, greater inflation pressure. An expandable tubular graft is positioned on the balloon, and the balloon is thereafter positioned within a body lumen adjacent a treatment site.
The balloon is inflated to the first inflation diameter to expand the tubular graft and thereafter inflation pressure is increased to the second inflation pressure such that the proximal and distal portions of the balloon inflate to the second, larger diameter, to further expand the proximal and distal portions of the tubular graft.
Further features and advantages of the present invention will become apparent to one of skill in the art in view of the Detailed Description of Preferred Embodiments which follows, when considered together with the attached drawings and claims.